1. Field of the Invention
The present invention relates to a JPEG decoder capable of scaling and a scaling method using the same, and more particularly, to a JPEG decoder having a scaling function, which scales and outputs an image file through the use of an inverse discrete cosine transform (IDCT) circuit included in the decoder, without a separate circuit for scaling, while increasing a decoding speed, and a scaling method using the JPEG decoder.
2. Description of the Related Art
Joint Photography Experts Group (JPEG) is an international standard for compression of still color images. JPEG compresses image information through the use of various algorithms, including Discrete Cosine Transform (DCT), Quantization, Variable Length Coding, etc.
Especially, JPEG is used in various fields, such as a digital camera, a mobile image sensor (CIS), etc., and recently, JPEG has been so widely used in a mobile field. When the conventional JPEG decoder for mobile is implemented with a general algorithm, the decoding speed is slow, which is not suitable for real-time output in mobile LCD displays.
Also, since the mobile LCD displays do not generally require a high output resolution, the mobile LCD displays employ a scheme of outputting an image of a low resolution through scaling.
For reference, although a high-resolution image provides a superior visual quality to that of a low-resolution image, it is necessary to use a low-resolution image in order to be matched with a bandwidth and other peripheral circuits.
An image scaling method employs a scheme in which most of. the entire scene of an image before scaling is maintained while the size of the image is reduced. Although the scene of an original image is completely remained in an image after scaling, the scaled image is expressed in a lower resolution. Most of general scaling schemes scale an image in such a manner as to equalize pixels with an equal weighting in a specific image area, and then to discard a predetermined part of the entire pixels in the area.
However, such a scaling scheme requires a separate functional block for scaling an image output from a JPEG decoder, thereby increasing the product size, and additionally increasing time required in a scaling block, which makes it impossible to output an image file in real time required, particularly in the mobile field.